Recycled polyester insulation (also called PET fibre or PES insulation) is made from post-consumer plastic bottles melted down and extruded into fibres. Brands like Thermawall, Superglass, and EcoTherm produce these rolls for the building trade — and they work well in campervans.
This review covers real-world performance in a UK van conversion.
Verdict
| Aspect | Rating |
|---|---|
| Thermal performance | ★★★☆☆ |
| Moisture handling | ★★★☆☆ |
| Installation ease | ★★★★☆ |
| Cost | ★★★★☆ |
| Eco-friendliness | ★★★★☆ |
| Overall | ★★★★☆ |
What It Is
PET insulation is a non-woven fibre mat made from recycled plastic bottles. The bottles are cleaned, shredded, melted, and extruded into fibres that are bonded together with a heat-set resin (typically bicomponent polyester fibres, not formaldehyde-based glue).
UK brands:
- Thermawall (made in Yorkshire from UK bottle waste)
- Superglass Multi-Roll (80% recycled glass + plastic)
- YBS Superquilt (multilayer, includes recycled fibre)
- Actis Hybris (multilayer with recycled content)
Thermal Performance
| Property | PET Fibre | Sheep's Wool | XPS Foam |
|---|---|---|---|
| Conductivity (W/mK) | 0.036-0.040 | 0.038-0.042 | 0.028-0.032 |
| R-value per 50mm | ~1.35 | ~1.30 | ~1.70 |
| Density | 15-25 kg/m³ | 20-35 kg/m³ | 25-40 kg/m³ |
PET fibre is very close to sheep's wool in thermal performance — slightly better in some tests, slightly worse in others. Neither matches XPS for pure insulation value per mm.
Moisture Handling
PET fibres are hydrophobic — they repel water rather than absorbing it. Water runs off the fibres rather than being absorbed into them.
Advantages:
- Does not absorb moisture, so it does not get heavy when damp
- Dries quickly if it gets wet
- Does not support mould or fungal growth
Disadvantages:
- Does not buffer humidity like sheep's wool
- Water that runs off the fibres collects at the bottom of the panel cavity
- A vapour barrier is even more critical than with wool
Installation
Pros:
- Cuts with scissors or a sharp knife — very easy
- No itching (unlike rockwool or glass fibre)
- Stays in place by friction — holds between panel ribs without adhesive
- Lightweight — about 15-20kg for a full van
- Comes in rolls 600mm and 1200mm wide (matches van panel rib spacing)
Cons:
- Can shed loose fibres during cutting
- Does not hold its shape as well as wool — can slump in vertical panels
- Thinner rolls often come in 50mm — you may need two layers for full coverage
- Not compression-resistant — avoid for floor insulation
Cost
| Material | Cost per m² (50mm) | Van coverage (30m²) |
|---|---|---|
| Thermawall PET 50mm | £10-14 | £300-420 |
| Sheep's wool 50mm | £14-18 | £420-540 |
| XPS foam 25mm | £5-8 | £150-240 |
PET fibre sits between XPS and sheep's wool in price — about 30% cheaper than wool.
Health and Safety
PET fibre insulation does not contain the respirable fibres found in rockwool or fibreglass. The fibres are thicker and less likely to become airborne. However, a dust mask is still recommended during cutting because the binder particles can irritate lungs.
Fire rating: Class 1 (BS 476). The polyester fibres melt rather than burn at high temperatures. It is not a fire hazard in a van build.
Vapour Barrier Requirements
Crucial: PET fibre needs a vapour barrier more than sheep's wool does. Because the fibres repel water, any moisture that reaches them condenses and runs down to the bottom of the cavity. Without a vapour barrier, this collects at the van's lowest panel point and causes rust.
Fit a 500-gauge polythene vapour barrier between the PET insulation and the interior wall board.
Environmental Comparison
| Factor | PET Fibre | Sheep's Wool | XPS |
|---|---|---|---|
| Recycled content | 60-100% | 0% | 0-20% |
| Biodegradable | No | Yes | No |
| Embodied energy (MJ/kg) | 15-25 | 10-15 | 60-80 |
| End of life | Recyclable | Compostable | Landfill |
PET insulation uses waste plastic and has a lower carbon footprint than XPS foam. It is not as green as sheep's wool, but significantly better than plastic foam.
Best Use Cases
PET fibre insulation is a solid mid-range option for van builds. It is cheaper than sheep's wool, easier to install, and uses recycled materials. The main limitation is moisture handling — it needs a meticulous vapour barrier.
Best for: Side walls and ceiling (50mm), where its flexibility helps conform to curves.
Avoid for: Floor (needs compression resistance) and wheel arch recesses (where a more mouldable material like wool or closed-cell foam works better).
Final verdict: PET fibre insulation is a good choice for budget-conscious eco-builders who are confident in their vapour barrier installation. At £300-400 for a full van, it offers the best balance of cost and environmental credentials among fibre insulations.
